Gas Phase Fuel Cells

Abstract

The invention provides gas phase fuel cells for use in such fuel cells and methods of operating such fuel cells.

1 . A method of operating a fuel cell system comprising a fuel cell assembly comprising: 
 an anode comprising a catalyst layer, a fuel entry port, a fuel flow field in fluid communication with said anode, and a fuel exhaust port;    a cathode comprising a catalyst layer, an oxidant entry port, an oxidant flow field in fluid communication with said cathode, and an oxidant exhaust port;    a polymer electrolyte membrane interposed between said anode and said cathode; and    an anode recirculation loop in fluid communication with said fuel exhaust port and said fuel inlet port;    wherein said method comprises:    (i) directing an oxidant stream to at least one said fuel cell cathode via said oxidant entry port;    (ii) directing gaseous methanol to a least one said fuel cell anode via said fuel entry port;    (iii) operating said fuel cell assembly so that water is produced at said cathode and carbon dioxide is produced at said anode; and    (iv) recirculating a the gaseous anode exhaust stream in said anode recirculation loop.    
   
   
       2 . The method of  claim 1  wherein the concentration of methanol in said recirculated gaseous anode exhaust stream is less than about 10 volume %.  
   
   
       3 . The method of  claim 1  where in the concentration of methanol in said recirculated gaseous anode exhaust stream is less than about 5 volume %.  
   
   
       4 . The method of  claim 1  further comprising venting at least a portion of said anode exhaust stream containing carbon dioxide during said recirculating.  
   
   
       5 . The method of  claim 4  wherein such venting is by a carbon dioxide separator or vent in fluid communication with said anode loop.  
   
   
       6 . The method of  claim 4  wherein said venting is by a pressure relief valve which is in fluid communication with said anode loop.  
   
   
       7 . The method of  claim 1  further comprising directing all or a portion of the water produced at said cathode to said anode by diffusion of such water through the polymer electrolyte membrane induced by a concentration gradient of water across said membrane.  
   
   
       8 . The method of  claim 7  where said cathode further comprises a cathode GDL having a through-plane water diffusivity that causes said directing of said water to and across said PEM.  
   
   
       9 . A method of operating a fuel cell system comprising at least one fuel cell assembly and a liquid methanol fuel supply, said method comprising 
 (a) vaporizing methanol from said liquid methanol fuel supply using waste heat from at least one said fuel cell assembly to form methanol gas;    (b) directing said methanol gas to at least one said fuel cell assembly.    
   
   
       10 . A method of operating a gas phase direct methanol fuel cell system comprising at least one fuel cell assembly, each assembly comprising an anode, a cathode and a polymer electrolyte membrane (PEM), the method comprising electrochemically oxidizing methanol at said anode, wherein the system is operated such that the primary source of water at said fuel cell anode is water produced at said cathode that diffuses through said PEM in an amount sufficient to humidify said PEM and provide water for the anode methanol oxidation reaction.  
   
   
       11 . A gas phase fuel cell system comprising: 
 (a) a fuel cell assembly comprising an MEA disposed between first and second fuel cell plates, wherein at least said first plate and the anode surface of said MEA define a fuel flow field having a fuel entry port and an exhaust port, and wherein said MEA comprises an anode GDL; a cathode GDL; a polymer electrolyte membrane (PEM) disposed between said anode GDL and said cathode GDL; an anode catalyst layer interposed between said anode GDL and said PEM, and a cathode catalyst layer interposed between said cathode GDL and said PEM; and    (b) an anode gas recirculation loop comprising (i) said fuel flow field(s), (ii) a conduit having a first end in fluid communication with the exhaust port(s), and a second end in fluid communication with said fuel entry port(s); and (iii) a vent between said first and second ends to vent gases from the anode loop.    
   
   
       12 . The fuel cell system of  claim 11  wherein when operating, waste heat from the electrochemical reaction within the fuel cell system facilitates vaporization of at least a portion of a liquid fuel to a gas.  
   
   
       13 . The fuel cell system of  claim 11  wherein said cathode GDL has restricted diffusivity to water so that when said MEA is used in an operating methanol gas phase fuel cell at least a portion of the water produced at the cathode diffuses across said PEM to the anode in an amount sufficient to humidify the PEM and provide water for the anode reaction.  
   
   
       14 . The fuel cell system of  claim 13  wherein about one-third of the water produced at the cathode diffuses to the anode.  
   
   
       15 . The fuel cell system of  claim 11  further confirming an anisotropic gas diffusion layer (GDL).  
   
   
       16 . The fuel cell system of  claim 15  wherein said anisotropic GDL comprises a plurality of gas diffusion pores in a first layer of conductive non-metallic material, wherein said first layer has increased gas diffusivity in at least a first direction.  
   
   
       17 . The fuel cell system of  claim 12  wherein said fuel is methanol.  
   
   
       18 . The fuel cell system of  claim 17  further comprising a methanol fuel source in fluid communication with said anode loop.  
   
   
       19 . The fuel cell system of  claim 18  further comprising a methanol sensor in fluid communication with the exhaust port(s) wherein the signal from said fuel sensor is used to control the flow of methanol from said fuel source to said anode loop.  
   
   
       20 . The fuel cell system of  claim 11  comprising a plurality of said fuel cell assemblies, wherein a splitter upstream from the fuel entry ports for said assemblies delivers substantially the same amount of fuel to each of said fuel cell assemblies during operation.  
   
   
       21 . A fuel cell comprising the fuel cell system of  claim 11 .  
   
   
       22 . An electronic device comprising the fuel cell of  claim 21 .  
   
   
       23 . A power supply comprising the fuel cell of  claim 21 .  
   
   
       24 . An electric motor comprising the fuel cell of  claim 21.